Connecting the innate and adaptive immune responses in mouse choroidal neovascularization via the anaphylatoxin C5a and γδT-cells.

Abstract

Purpose : Neovascular age-related macular degeneration (AMD) is characterized by choroidal neovascularization (CNV). An overactive complement system is thought to contribute to AMD pathogenesis, and serum pro-inflammatory cytokines, including IL-17, are elevated in AMD patients. IL-17 is produced by anaphylatoxin C5a receptor-expressing T-cells. Here we asked whether C5a generated locally in response to CNV recruits IL-17-producing T-cells to the eye.

Methods : CNV lesions were generated in C57BL/6 mice using laser photocoagulation in the presence and absence of anti-C5, anti-C5a, or 12B4 (control) blocking antibodies. CNV lesions were quantified by optical coherence tomography; and T-lymphocytes were characterized by QRT-PCR.

Results : CNV resulted in an increase in splenic IL-17-producing γδT- and Th17-cells; yet in the CNV eye, only elevated levels of γδT-cells could be observed. Administration of anti-C5 or anti-C5a-blocking antibodies to reduce levels of C5a production in the eye, blunted the CNV-induced production of splenic Th17- and γδT-cells, reduced CNV size (anti-C5: 3666 ± 359.9 pixels; anti-C5a: 3453 ± 253.8) when compared to control (12B4: 5572 ± 630.6; p ≤ 0.01) and eliminated ocular γδT-cell infiltration. In ARPE-19 cell monolayers, IL-17 triggered a pro-inflammatory state; and T-cell proliferation was elevated in response to ocular proteins

Conclusions : Taken together, we demonstrated that CNV lesions trigger a systemic immune response, augmenting local ocular inflammation via the infiltration of IL-17-producing γδT-cells, which are presumably recruited to the eye in a C5a-dependent manner. Finally, understanding complement-mediated pathological mechanisms will aid in the development of a treatment for AMD.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.